Preheat oven to 375°F.
Grease a 9x13 casserole dish or large baking dish.
Place chicken breasts in an even layer in the dish.
In a small bowl, whisk together mayonnaise, 1/2 cup parmesan cheese, minced garlic, garlic salt, and freshly cracked pepper.
Spread the mixture evenly over the chicken breasts.
Sprinkle remaining 1 cup parmesan cheese over the top of the chicken.
Bake for 40 minutes, or until an instant-read thermometer reads 165°F internally.
Remove from oven and garnish with chopped parsley if desired.
Serve hot.